that
they make uniform contact with commutator over the whole surface.
3)
Inspect commutator every 500Hr of run.
If
affected, polish clean with
#400
sand paper and wipe with clean cloth wetted with gasoline.
Mica
pieces must be
0.6-0.8mm
below commutator surface.
If
out, undercut them accordingly.
6-2 A.C. Generator
Fr.
bracket
Fig.3-42 Generator Section (A.C. generator)
This A.C. generator
is,
differently from a conventional
D.C.
unit, built so
that
the
armature
is
installed outside and the field
is
turned inside
as
a rotor. It features, among
others, an extremely long service life
of
the brushes and ability
to
operate
at
a very high
r.p.m., because the arrangement dispenses with commutators and subjects the brushes
only
to
a small current, while its field has very simple make-up
as
compared with the
armature
of
a
D.C.
generator
and
it
is
free frpm the need of commutation.
The construction of the A.C. generator
is
illustrated
in
Fig.3-42 Revolution of the
field generates a three-phse alternating current
in
the armature, which
is
rectified by
silicon diodes installed
in
the rear bracket and supplied at D terminal. The field circuit
is
electrified
at
F terminal from the battery through field relay and relay, the current
running,
on
one part, from brush
to
the field coil through slip ring and on the other,
to
E terminal through the other brush and slip
ring.
Having
silicon diodes, the generator
cannot make
self·starting
as
a
D.C.
unit does
by
residual magnetism of the field coil, so
is
excited
to
start from the battery.
-
52-
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